Artist’s rendition of Paludohadros proudlovii (with a Baryonyx in the background). Credit: Guilherme Gehr

Britain’s dinosaurs are multiplying, and scientists don’t even need to dig for some of them.

For decades, palaeontologists thought they had a reasonably good picture of the enormous plant-eating dinosaurs that roamed southern England 125 million years ago. Turns out, they’ve been missing a few things.

The latest addition is Paludohadros proudlovii, a herbivore about as heavy as a large hippo. The dinosaur’s bones have spent roughly 25 years in the Natural History Museum’s collections before researchers realized they belonged to an entirely new species and genus.

Turns out, Paludohadros’ fossil lay just 100 metres from those of Baryonyx, a famous spinosaurid known to have eaten young dinosaurs from the same broader group.

The Great Iguanodon Mix-Up

Iguanodontids can look very much alike. Artistic renderings of Iguanodon and Mantellisaurus. Credit: Wikimedia Commons

For much of the past century, large iguanodontian fossils from southern England were usually assigned to either the bulky Iguanodon or the more slender Mantellisaurus.

But a 2023 anatomical reassessment of Mantellisaurus helped researchers distinguish features that had previously gone overlooked. Other investigations have revealed a succession of different dinosaurs: the bulbous-nosed Brighstoneus in 2021, Comptonatus in 2024, and the sail-backed Istiorachis in 2025.

These discoveries have been rewriting the family tree of Britain’s plant-eating dinosaurs. And the latest addition was hiding in plain sight.

Artistic renderings of Brighstoneus (left) and Comptonatus (right). They’re easily mistakable for one another. Credit: Wikimedia Commons
But not Istiorachis. He’s really cool. Artistic rendering. Credit: Wikimedia Commons

In July 2001, amateur geologist Geoff Toye discovered a partial skeleton during a geological field trip to Surrey’s Smokejacks brickworks, also known as Ewhurst Works. He donated the fossils to London’s Natural History Museum, where they remained in the collections for the next 25 years.

It wasn’t until researchers led by Ricardo Sacamoto, a PhD student at the Natural History Museum, carefully re-examined the bones and compared them with other iguanodontians that their true significance emerged.

They found several distinctive features.

Its upper arm bone had unusual ridges near the elbow, while its shinbone displayed bony bumps near the knee and a prominent rectangular crest near the ankle. Perhaps most revealing was its ischium, one of the bones forming the pelvis. Unlike its relatives, Paludohadros had a curved ischium with two overlapping ridges along its shaft, as well as an enlarged tip.

Together, these anatomical signatures distinguished the specimen from Iguanodon, Mantellisaurus, and other known relatives, providing the evidence needed to establish a new genus and species.

And once researchers knew what to look for, they started recognizing the dinosaur elsewhere.

They identified upper arm and shinbones with the same distinctive features among fossils collected at the Surrey quarry in the 1950s. Apparently, workers there had dug up the species decades before scientists gave it a name.

Even more intriguingly, a separate hip bone recovered from the same quarry in 1983 differs significantly from that of Paludohadros. It could belong to yet another iguanodontian species that scientists haven’t identified.

So how many different dinosaurs actually lived in prehistoric southern England? And did all these newly named species roam the same landscapes together?

Not necessarily. Their fossils come from different geological formations and sedimentary basins. The Isle of Wight preserved seasonal river floodplains, while parts of mainland southern England contained lakes, mudflats, and swamps.

Scientists aren’t yet sure why dinosaurs found in these regions differ so much from one another. They may have occupied different habitats, been separated by geographical barriers, or simply lived at different times.

The Stout Swamp-Dweller

At roughly 5 metres long and 1.5 to 2 tons, Paludohadros weighed about as much as a large adult hippo. Yet its bones appear to have been incompletely developed, suggesting this specimen was still immature. A fully grown animal may have reached considerably greater proportions, potentially twice its size.

Paludohadros proudlovii – human – hippo size comparison. Credit: ZME Science

It was a heavy-bodied, four-legged plant-eater, with a gently rounded snout ending in a toothless beak. Rows of ridged, diamond-shaped cheek teeth helped it chew vegetation. Like its relatives, it would have had a long tail, and its hands bore pointed thumb spikes. One spike actually survives among the fossils, complete with grooves where a protective keratinous sheath likely attached.

Paludohadros roughly translates to “stout swamp-dweller,” combining the Latin word palus (swamp), with the Greek hadros (stout/bulky). It’s a nod to the muddy wetlands that it inhabited 125 million years ago.

The researchers named the species proudlovii in honour of Will Proudlove, the former manager of the Surrey brickworks where they discovered the fossils. Proudlove rose through the company’s ranks to become manager and took a keen interest in the prehistoric fossils that workers occasionally uncovered while excavating clay.

Tragically, Proudlove died in 2000, leaving behind his wife, Rachael, and their two young children, Ellie and Matt. Just a year later, Geoff Toye discovered the dinosaur’s fossils at the quarry.

“Will always had an interest in dinosaur fossils and was fascinated about what, if anything, would be uncovered each time a layer of clay was removed from the quarry,” Rachael Proudlove said in a statement. “Sadly, this dinosaur was only discovered the year after he died, but its story has become a part of our lives since then.” She added: “We’re absolutely overjoyed and honoured that Will’s name and legacy will live on in this dinosaur.”

The Spinosaur Next Door

Artistic rendering of Baryonyx. Credit: Wikimedia Commons

In 1983, fossil hunters uncovered Baryonyx walkeri at the very same Surrey brickworks. This large spinosaurid had crocodile-like jaws, powerful forelimbs, and gigantic curved claws. Remarkably, paleontologists found its remains just 100 metres from where they would later discover Paludohadros, in deposits belonging to the same geological formation.

And there’s good reason to suspect the two dinosaurs may have interacted.

“While Baryonyx is best known for eating fish, this dinosaur’s last meal also included a baby iguanodontian,” said Susannah Maidment, the study’s senior author, in a statement.

A 1997 examination of the predator’s fossils documented iguanodontian bones in its abdominal region, offering rare direct evidence of what Baryonyx ate.

Iguanodontid femur found within the rib cage of a B. walkeri. Credit: Wikimedia Commons

Could that unfortunate youngster have been a Paludohadros? Maidment says it’s possible that Baryonyx hunted young members of the newly identified species or scavenged their carcasses. But the bones cannot establish the prey’s identity.

Still, the discovery helps bring this ancient ecosystem into sharper focus. What once looked like a landscape dominated by a handful of familiar plant-eaters is revealing a much richer cast of dinosaurs, complete with predators that may have hunted them.

And the story is far from finished.

“I’m now going to go through the Natural History Museum’s iguanodontian collections to identify what’s there as part of my PhD,” lead researcher Ricardo Sacamoto said in the museum’s announcement. “This could lead to the discovery of more new dinosaur species that haven’t yet been recognised.”

Scientists may have already excavated some of Britain’s dinosaurs without realizing they belong to previously unknown species. They’re simply waiting for scientists to recognize them.

The study was published in the Journal of Systematic Palaeontology.